My son rolled from his back to his tummy last night and has also rolled from his back to his side before. He’s only two months old so I am guessing this rolling isn’t intentional. He moves around a lot during tummy time and gets up some momentum but hasn’t shown any signs of rolling tummy to back. Do we now need to have his arms out of his sleeping bag and transition him to a cot?

While most babies do not roll before 4-5 months, some roll earlier.
It is difficult to know if this is intentional or accidental.
Some babies will wriggle & squirm from a very young age & for some of these babies, they prefer their arms free & like to touch their face &/or suck on fingers.

I think it would be important to manage him as if he is rolling & to cease swaddling (arms out of swaddle suit) at the least & preferably move him to his cot now as well.
Babies need their arms free & the space of the cot to roll well.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

Red Nose recommends to have baby “arms free” from 3 months of age in preparation for rolling.
https://rednose.org.au/article/wrapping-babies - longish article but scroll down to “principles of safe wrapping”