I kinda agree, I believe 29k lb thrust is a deliberately low figure given as a possibility by using the word 'can'. It doesn't mean that that is its max thrust.
I wouldn't take the quote too seriously.
In the same quote, they say:
"The J-10C can produce 29,000 lb thrust, which is 10,000 lbs excess thrust than the JF-17 produces, and as much power as two and a half Mirages put together. A single Mirage produces 14,000 lb thrust"
Two and a half x 14,000 lbs = 35,000 lbs
And 35,000 lbs is obviously lower than 29,000lbs.
So I don't think they are being too careful with the real numbers lol