Asra is actually the only one who knows that Thomas was made of flowers
he found out by accident while Thomas was recovering from his resurrection, when he went snooping through Thomas’s uncle’s books to see if there was any information there that would really go into the consequences of bringing someone back to life
what he finds is a lifetime’s worth of journals, which all read as the account of a doting uncle...if not for the first entry describing how he made Thomas out of flowers in the woods at the end of spring.
beginning to end, Thomas has always been some kind of magic experiment. but it at least explains his weird affinity for plants