They were in the studio together, so signs point to it being a possibility.
We don't have a whole lot of context for this, but if a tweet from Memphis May Fire is anything to go by, there's a chance that a collaboration with Post Malone is in the works. Memphis May Fire frontman Matty Mullins apparently caught up with Post Malone last night, and snapped a sneaky pic with him, posting it to twitter with the caption "Fun times as Matty Mullins caught up with Post Malone last night. Future collab??".