According to Merriam Webster, bestiality is defined as follows:
"Sexual relations between a human being and a lower animal"
I find the phrasing "lower animal" to clearly imply that intelligence is a factor in the matter. For example, a human and a human-intelligence feral dragon should be marked anthro_on_feral (or vice versa), but not as bestiality, because the dragon is in this case not a "lower" animal.
Bestiality should be a tag reserved for cases in which the feral animal is not clearly a sentient and intelligent agent.