Yes they are different, but WES just compares it, they gave me in writing hence I have advised. I got my masters degree as diploma from them too, so had to reach out to them to clarify- same issue my batch mate who is a CA citizen now got it as Masters some 6 years back but I didn’t. Hard times! I have applied with Toronto CES now as per someone’s advice, it gives me additional points and being at 457 currently leaves with no option than to explore every possible option..
And.. you are correct - as per my research in 2018, I also found out that WES used to write Master for an IIM PG diploma but no more as technically it is not a master degree.