Because I lack science in all respects.
0.62 atm (O2 52%,N2 39%,Ar 4%,Kr 3%)
0.36g (gravity), Temp: 286K/13C
There's no CO2; others have pointed it out. Most likely, the report is incomplete: CO2 is only about 0.04% of Earth's atmosphere, and you have 2% of your atmosphere not accounted for, possibly unmentioned trace gases including CO2.
There's one heck of a lot of oxygen, even given the low pressure. Oxygen just loves combining with things; unless something's producing it, it'd combine out, ergo something's producing a whole lotta oxygen. If there's no CO2, that something is not a plant: plants take in CO2 when making O2, and there's no CO2 for them to take in. If - as is most likely - there is CO2 but it just didn't make it into the report, there's either one heck of a lot of O2 producing life or there's some O2 producing process in addition to the local life. A lot of Earth's O2 comes from the oceans - phytoplankton, algae. Warmer oceans? The planet overall is a bit cooler on average; maybe the equatorial belt is dominated by ocean; land masses are above and below that.
There's about 4 times as much argon as shows up in Earth's atmosphere. Most of our argon comes from decay of radioactive potassium; this world has more radioactive potassium than we have here.
There's several orders of magnitude more krypton in the atmosphere than in Earth's - I mean, tens of thousands of times more. Krypton has quite a few isotopes. I haven't the foggiest where the stable ones come from nor how they'd get into an atmosphere in such quantities. Most of the unstable ones have really short half lives thatcouldn't account for this. There is one with a half life of about 10 years; it's produced by fission of uranium, and it could possibly be the culprit. One possibility therefore is this planet has one whopping lot of uranium, in quantities sufficient to permit natural fission. The other is that this planet was very recently blasted to hell and gone with nuclear weapons - or the planet is a target range where the IN practices nuclear bombardment. Seems kinda pricey, but maybe there's specific study that needs actual bombs to go off.
So, very speculative, but: you've got a coolish world where the equatorial region is mostly water, lots of algae and other O2 producers in the seas, and the land area was recently subjected to a ferocious nuclear bombardment. It is probably not healthy to spend much time on land here.