It wasn't just that. Mendocino wasn't a low bin, it was an entirely separate die from Pentium II. At the time, Pentium II used a 512kB off-die L2 cache, running at half cpu clock. To save on costs, Celeron 300A moved to a 128kB L2, which was integrated on the CPU die, and which ran at full cpu clock.

And it turns out that for a lot of software, a smaller but faster L2 was actually better than the bigger one. And because there were no fast products that used the Mendocino die, even the fastest of them were sold as Celerons. 300A was particularly nice because very nearly all of them could run at 450, and 100MHz FSB motherboards were widely available to pair with the fixed 4.5 multiplier of the CPU.