You could say things like that with anything in percentages? 100% increase in your pension from 100k to 200k is only 10% (increase, to 20% total) of your target 1M, or whatever.
The equivalent would be saying that going from 600k to 700k was a 100% increase... compared to 500k.
It's not completely meaningless, to be fair. Saying 10°C to 20°C is a 100% increase has the meaning of "it's twice as far from freezing", which isn't totally meaningless (kind of like saying Everest is twice as high as Mont Blanc, which really means "its summit is twice as far from sea level").
If your ”whatever” target instead was 50k, is the argument that going from 100k to 200k would be 400%?
If the argument was saying there's something special about 100% being 100 quantity then.. no? I don't really know where to go from there, what I said still holds with a 100k target, but I'm not going to be able to give 'another' example where the 100 quantity is meaningful because it isn't for degrees either. It's the freezing point at 0 that makes it work better for centigrade than Fahrenheit, imo.