It’s pretty unlikely he lied about the makeup of the Britons’ army, because that could be seen (and heard, they made a racket after all) and verified at very least by anyone in the front ranks of the Romans. So there is no point in outright lying there, at best he could get away with a slight exaggeration.

This is the only point I actually disagree with - the presence of any significant number of women in the enemy army, even far short of a majority, would give him a pass to say something along those lines. Roman society was deeply misogynist and regarded women in combat as an immensely ‘barbaric’ practice, so it was an easy ‘point’ to score. Overplaying an enemy’s real flaws (or things that are perceived as flaws) compared to a strictly objective assessment is a classic rhetorical technique - and the Romans regarded rhetoric as a practical art worth learning!

The Roman army at that time were professional soldiers very well trained in all aspects of war and soldiering, and very well equipped with the finest state of the art kit the res publica could buy for them. Their opponents were mostly just regular people who took up arms, had to use whatever equipment they could personally afford, and, at best, had as much military training they could do in their spare time besides having to make a living.

It was even worse than usual for the Britons at this point - they’d been occupied for some 15 years, and had very little opportunity to practice warfare. The Romans cracked down on war that didn’t involve them (they were very particular about that!) and were unlikely to look kindly on client kings having regular military drills practicing calling on their tribal vassals - very suspicious looking! On top of that, many young Briton men had volunteered or been conscripted for the auxiliaries, meaning probably the best candidates for soldiering were already in service to the Romans and many of them likely posted halfway across the Empire (though this wouldn’t become standard practice for a few more years).

It’s more than just instructions, it’s the ultimate reassurance that everything will be alright, because he basically could have just read that from a “How to Roman legionary for dummies” textbook. Actually I wouldn’t even be surprised if he directly quoted that from a training manual. It’s like saying “Stick with your training and everything will be fine”.

“Remember your training, lads!”

Though to be fair, legionaries did practice a wide variety of tactics, so one could argue that here he is giving circumstance-specific, if still general-in-details, advice.

They’re outnumbered and Paullinus positioned the troops on a narrow front with natural obstacles to cover them - ‘Stick together’. Stay bunched up, maximize concentration of force against an enemy that can’t do the same. ‘Throw the javelins’ could be understood as implying that even the rear ranks should throw before the clash - legionaries were sometimes noted as throwing javelins at harassing troops or in skirmishes as the battle wore on, suggesting that not everyone always threw before the main clash as standard practice. ‘Push forward’ is certainly Paulinus encouraging pursuit over a defensive posture. ‘Knock them down with your shields and finish them off with your swords’ may not have been the advice were they against heavy infantry, trained and disciplined forces, or cavalry.

He might have advised them to keep their spacing, as Caesar did in one of the battles of the Gallic Wars, to maintain their ability to maneuver and engage individual targets. Or to retain their javelins to lob at harassing light cavalry or to use as a spear against heavy cavalry, as was sometimes noted against the Numidians and Persians, respectively. Or to hold their ground, as was often ordered against Germanic tribes to avoid being drawn into an ambush or getting legionaries strung out over wooded areas. Or to focus on swordsmanship instead of brute force and weight, as was noted against some Gallic tribes and in civil wars between legionary forces.

Certainly instructions they were trained for, but instructions all the same! Arguably. Admittedly, also arguably it could have been just to remind them that they’re part of a military machine that has demonstrably consistent success even against significant foes, so long as its parts remember to operate as-usual, like you said.