It seems strange to believe that they could've been unaware of radiation risk in the area when doing that; radioactivity warnings should be widely visible.
There were allegedly fires[1][2] in the forest recently, and there is the possibility that vehicles driving through the area kicked up radioactive dust[3].
Russian forces may be starting to withdraw[4] from the Chernobyl site.
[1] - https://www.mirror.co.uk/news/world-news/breaking-chernobyl-...
[2] - https://www.ibtimes.co.uk/forest-fire-engulfs-more-10000-hec...
[3] - https://www.reuters.com/world/europe/unprotected-russian-sol...