Post hoc ergo propter hoc means "after this therefore because of this". The name of the fallacy is the claim the arguer is making, that because one event happened soon after another event, it was caused by the earlier event. A common example is that deciduous trees lose their leaves after it gets cold, so they lose their leaves because it gets cold. The actual reason is complex and has little to do with temperature. It's partly that day lengths get shorter and the leaves no longer can absorb enough energy to match their costs.

It is similar to correlation doesn't equal causation, but is more specific that it has to do with two events that happen at similar times, which is specifically called out in the tweet.

That the argument is heuristic and not logical is that logic has a pretty limited use - where you can reasonably agree on premises to make a specific type of argument that relies on how that argument is constructed. Heuristics rely on probability, what's the most likely outcome given a set of preceding causes, or what are the most likely causes given a following event. For example most problems in my line of work are from loose connections, so it's the first thing I look for when something is going wrong. You can't say "because I see this event it is logically this cause" but you can say "When I've seen this event before 80% of the time it was cause A, 15% of the time it was cause B, and 5% of the time it was cause C. So I'll check them in order of likelihood"

So the tweet isn't making a logical claim. They're saying it's unlikely that Trump talked to Putin about informants, requested the list of informants, had a list of informants in an unsecured place, but somehow wasn't related to those informants being compromised.

EDIT: Also Wikipedia has a better explanation of pheph: https://en.m.wikipedia.org/wiki/Post_hoc_ergo_propter_hoc