Homo-romantic friendship...? Or it explores the nature of isolation and how attachment to others can intensify the frustration that it looks romantic. Considering the author said herself she never intended Nettaigyo to be Yuri romance, and the angst surrounding this 'frienship'--especially the lizard and frog metaphor or allusion--maybe tackling intense feelings of isolation is the point.
We may wear whatever goggles we like while reading, as long as the author has already said her piece, readers' expectation and interpretation of fictional characters--however it matters still--comes in second place.