I've had similar case - 4 peasants became legendary wrestlers in 1 season (maybe 4-5 months, wasn't watching them that closely).
Fort was sealed, so that couldn't have been zombie choking case. Training them as champion hammerdwarfs took much more time (about 1 year)
edit:
Mining:
I've started fresh fort, all dwarfs had no skill. One of them was mining sand. I've kept him fresh using dwarf companion, so he was digging all the time. He reached legendary level on 3rd Hematite, so it took him exactly 1 season. He dug 1800 tiles confirming wiki information on exp/tile rate.
Side note:
Other dwarfs were just sitting on wagon socializing themselves... and they gained 11000-12000 exp points from that (4 attribute increases! ). All were ecstatic from talking with their lovers/friends, even though they were caught by snowstorm and rain, slept in dirt, had neither chairs nor tables... weird.
Wrestling without armor:
Fresh fort started, I've build 1 bed and dug small room for barracks. Dwarf Companion was used only once (healing spine wound). No armor and no weapons used.
Training started: 9th Granite
First elite wrestler: 1st Slate (19 days)
Last elite wrestler: 17th Slate (34 days)
date of becoming champion:
21st Slate (38 days)
26th Slate (43 days)
28th Slate (45 days)
2nd Felsite*3 (49 days)
9th Felsite (56 days)
Average time: 47 days
Wrestling in armor:
Fresh fort, 1 bed, small room digged. Starting points modded using Gibbed's Tweak.
Armor: steel chain mail, steel helmet, steel gauntlets, steel low boots, steel greaves.
shield: steel shield
Training started: 4th Granite
First Elite wrestler: 18th Slate (42 days)
Last Elite wrestler:4th Felsite (56 days)
date of becoming champion:
4th Felsite (56 days)
5th Felsite (57 days)
11th Felsite (63 days)
15th Felsite (67 days)
23rd Felsite (75 days)
25th Felsite*2 (77 days)
Average time: 67,5 days
Hammerdwarfs with armor:
Training started: 5th granite
first Hammer Lord: 21st Limestone (184 days)
I think it's pointless to continue training - it's obvious it takes much more time. I estimate, that training in wrestling gives ~5-7 times more xp.