I’m not a scientist, so I could be interpreting this incorrectly. The results of the one comparative study that supported HTH transmission are as follows:

Of 476 household contacts, 16 (3.4%) developed HPS; 32.6% of the 92 cases occurred in 14 household clusters. 460/476 contacts remained seronegative. The risk of HCPS was 17.6% among sex partners of index case patients vs 1.2% among other household contacts (P < .001). For sex partners: adjusted OR, 9.71 (95% CI, 1.72–54.67). For exposure to saliva (deep kissing): adjusted OR, 5.05 (95% CI, .89–28.52). Human-to-human transmission appeared definite in 3 (ie, no environmental co-exposure, urban residence), probable in 9 (ie, close contact with the index case patient, including 7 of 9 who were sex partners, and a lack of major risk factors for environmental exposure), and possible in 2 of the 16 additional household case patients. The remaining 2 had a shared environmental exposure.

They ding that for not having an unexposed group (that’s their only serious RoB, but their overall score is serious), but also mention this:

The RoB in included studies is a particular concern when trying to determine whether human-to-human transmission of hantavirus is the best explanation for infection in other human contacts. A randomized controlled trial, where subjects are randomized to exposure to another human with hantavirus or to a nonexposure control group, in theory, would constitute the ideal study design. However, ethical and feasibility concerns make this kind of study impractical at this stage of our understanding of the problem.

Which makes sense, given the potential mortality rate, but it seems like the only serious issue with that study.

Then, half of the total noncomparative studies showed at least some evidence for HTH-transmission (no evidence in studies from outside of Argentina and Chile, but 7/9 for those from those countries). In those studies, there were a maximum of 12 cases wherein researchers found

identical [viral DNA] sequences but likely different geographic area of infection

Which seems pretty firm to me, but again, I’m not a scientist and I don’t want to fearmonger. It seems like this could be easily explained if there are some strains that are passable between humans and some that aren’t. I absolutely understand the authors of this study coming to the conclusion that it may be transmissible between humans, but it’s not definitive, because science should be rigorous and thorough. If I have understood it correctly though, this seems conclusive enough for me to behave as if this were contagious, out of an abundance of caution.

It definitely seems like it would mostly be through heavy exposure (intimate contact or prolonged tongue kissing), which is reassuring.

Edit: that downvote was unintentional, I was glad to read your comment and found the study quite engrossing for having no familiarity with the subject matter, outside of having been a news addicted adult during covid