Because something is printed in RT doesn't make it untrue. That something - critical of Russia's enemies - is only reported in RT and not in any other major new source - is a strong contender for being untrue.
For something to an example of the ad-hominem fallacy, it has to be discarded purely on the basis of the claimant. If something is being rejected on the basis that the claimant is unreliable and contradicts generally reliable sources, that is something quite different.
Should I start discounting RTs weather report for NYC based on their political reporting feel free to call me out on fallacious thinking.
You may be right, but your logic is fallacious. If there's only one news source and that news source is biased, then it doesn't follow that anything they say is untrue.
You are calling something false based on the source. This is simply illogical: a broken clock is right twice a day. Following your reasoning it would be wrong even when right.
Either the news is true or it isn't. Judge it based on its own merits, not from its source.
For something to an example of the ad-hominem fallacy, it has to be discarded purely on the basis of the claimant. If something is being rejected on the basis that the claimant is unreliable and contradicts generally reliable sources, that is something quite different.
Should I start discounting RTs weather report for NYC based on their political reporting feel free to call me out on fallacious thinking.