Tower Controller reported a possible minimum vectoring altitude violation due to a miscommunication in regards to the assigned altitude of a go around instruction.

Narrative

I was working Local Control. We were in an unusual; complex configuration due to an airshow. It had been precoordinated that; for the special configuration; ZZZ TRACON MUST provide 20 miles in trail to RWY XXL with standard separation to RWY XXR. ZZZ TRACON was running 4-6MIT in trail to RWY XXL with no one landing RWY XXR. It was exceptionally difficult to manage the existing traffic and depart RWY XXL; which had an abnormally high number of departures due to the configuration. In addition; all of the destinations that typically have CFR programs were being sent to RWY XXL. We attempted to adjust a CFR flow time due to being unable to depart and the aircraft ended up with an additional 20 to 30 minute delay on top of what they already had received. With limited space and places to put aircraft; I crossed the aircraft to hold between the runways; which was the only available spot to hold an aircraft due to traffic waiting for both RWY XXR and RWY XXL. The following 3 to 5 aircraft also had flow times and with an already complex operation. In order to not run the risk of the other aircraft receiving delays and blocking and preventing any and all departures; given that the next 5 to 7 aircraft were tightly in trail to RWY XXL; I sent Aircraft X around on check in; approximately 5 mile final.I gave the pilots of Aircraft X; a standard go-around of 'turn left to heading 260; maintain 031.' I completed several other tasks and then; before shipping the aircraft to departure; observed the heading and altitude to be appropriate. Heading 260 and 2600 ft. at the moment of transfer of communications; given the instructions; and shipped them to departure. Later; when the aircraft came back around; the pilot asked for the tower phone number and called the tower. It was then that I learned that there was an issue with their altitude and a possible MVA violation. The pilot stated that they were given 'H260; M026' and were upset about the proximity to terrain. When we listened to and watched the playback; it was hard to differentiate whether they read back M021 or M031; which; either way; was not what they complied with. And watching the playback; they were level at 2600 ft. for a little while before shipping the aircraft; but the aircraft never inquired about the altitude with the tower.Suggestion: Despite a culture of ZZZ TRACON not advising us when an aircraft is not on the advertised approach and also some controllers and management not wanting the published missed to be issued; I am going to go back to issuing that; since it is nearly identical to what we assign manually; but it leaves less room for ambiguity; poor/mistaken readbacks; and hearback issues. Furthermore; while it is not everyone in Area B at ZZZ; there is a culture of ignoring procedures; LOAs (Letter of Agreement); and prearranged coordination when it comes to arrivals and runway assignments; even when there is an extreme need for help and adherence to the rules and coordinations due to complexity or traffic needs. This is something that has been discussed at length and clearly there is a systemic lack of understanding; caring; and or ability on that side.