Yes. Well. Sure. Surprising? Not so much.

I think it was as long ago as 1979 (Hodges and Moore) that the formation of Olympus Mons was hypothesized to have occurred in ice, assumed to be water ice, not carbon dioxide, and that many of the features we see such as the aureole and the 10km high escarpment (imagine the close up visuals) are the result of its icy origin. There's also a large outflow region to the west of Olympus, all of which strongly implies the presence of water -- fluid of some sort -- during the formation of Olympus -- ie: volcanic heat + ice = some flowing water as a rule.

Present day subsurface water (or comparable fluid) at this site would be implied unless for some reason all the water/ice once here has migrated elsewhere.

The clay hypothesized by McGovern and Morgan would be strongly suspected in the region prior to and during the formation of the Tharsis volcanoes even without the modeling they do, but it's interesting that they see other surface expressions on Olympus of its icy/watery/clayey origins. All to the good.

Does this imply biology? Not necessarily. One of the persistent problems in considering that question is an overreliance on the assumption that water is the principle fluid on and under the surface. Many signs point to the fact that fluid relatively pure water may actually be quite rare on Mars, and that the more common fluid is sulfuric acid, with other equally salty and/or acidic aqueous compounds underground and occasionally at the surface.

Hardy biology might well adapt and thrive under the circumstances. Examples on Earth of acid loving microbes aren't common, but they exist, and there's no reason to think they couldn't exist and thrive on Mars. Part of the key is to set to the side the premise that biology on Mars would arise and evolve under purely watery conditions and think instead of how (and whether) Martian biology could develop under the highly salty/acidic conditions that may have been more prevalent and might still prevail beneath the surface.