Mina, first place in S league has all glyphs max level, on entire team. This means around 400k exp for each glyph. Notice that all glyphs are legendary on all 4 heroes.
Because epic mine crystal activations produce essence at a much higher rate than any other activation, and produce a very high rate of xp glyphs, that’s feasible if you want to spend enough. About 100 activations would be enough to max out a legendary stat glyph, and would almost certainly give you enough essence to buy a legendary glyph. 85 should be enough for a skill glyph
Mina has 12 maxed out (or close to it) stat glyphs, so call that 1200 activations, and 3 maxed out skill glyphs for another 255 activations. The maxed are rares are trivial in comparison.
Add up all the crystals, and that is 291K, just over $400 of crystals. Considering Mina is a little short of completely maxed out, I think it is completely feasible that they simply bought $400 in crystals and used them on epic mine activations.
As long as the purchases are confirmed to be legitimate, it just takes a few days of clicking mine activations over and over to get there.