I believe you're correct, at least from the comment there:

	    bit 5:
	        0 = /RTS set to 1
	        1 = /RTS set to 0

Which says that /RTS (inverted RTS by typographical convention) is 1 when the bit is 0, so plain RTS is 0 when the bit is 0.

But the code does:

m_rts_handler(!BIT(data, 5));

which is the opposite.