Kay, so lets say some dude decided to spam frags in the 67thway barn, everyone successfully dodges it, except mr. bork comes in and throws the live frag at the innos with his handy dandy magneto stick. would mr bork be technically meta gaming by helping traitors get kills???
If you personally throw the grenade at players with a magneto stick who were not going to be damaged by it, and as a result they take damage, you are technically at fault for the damage done to them, and with an admins discretion, you can and will be slain. However, your question on whether or not this is metagaming is tricky. If your intention is to damage innocents and have the traitors grenade damage innocents, then yes, you are technically working against the win condition of the innocent players and you could possibly be charged with metagaming. However, if your intent is just to get the grenade away from innocents, and your plan ends up backfiring, you may or may not be at fault for the deaths depending on the situation and circumstances, but it is definitely not metagaming in this instance, so like always it just depends on the intent and the situation. Situations like these are handled by administrators because of how often they vary based on situation. Here is a link to a relevant forum report on a topic that follows this same line of logic back from 2015: https://www.seriousgmod.com/threads/report-against-drunk-dog.23469/
What if I'm doing it with the intent of saving my own life, and just chucked it in a direction as fast as I could?