"A 1.8C difference" expands as "A difference of 1.8C" expands as, and here's the ambiguity, either:

"An absolute difference of 1.8C, or 274.8K, measured between A and B"

or

"A relative difference of 1.8C, or 1.8K, is added/subtracted to A/B in order to reach B/A"

I don't think the context-free variant with K will improve understanding and decrease confusability in this discussion context, but I appreciate the pointer about it in general. I'll take a lot more care around it in a future thread about space apparel!