IMO, the bolded is 99% the more likely cause of his missing practice.
The crosscheck just wasn’t anything that could cause a meaningful injury. There was no real collision, it wasn’t to an area that could easily be broken, no joints involved, and he was visibly not injured when he chased Sprong. If it was something like back spasms afterward, then those spasms were probably going to happen on the next hit regardless. IMO, this is a case where something just stuck in people’s memories and so it was top of mind when he turned up missing in practice.
A contact injury to the leg, on the other hand, is exactly the kind of thing that a player can skate through for a couple of periods. It’ll hurt and swell but that’s nothing they can’t deal with in the trainer’s room. It’s not till the next day that you think, yeah I shouldn’t be skating on this. It may even just be a precautionary rest, because why make it worse on purpose.
I wouldn’t read too much into any of it considering he walked off the ice looking fine.