Simplex means radio to radio and not going though a repeater. When operating a repeater, you key the mic and it transmits on the repeater's input; then when you un-key the mic,the radio will "listen" on the repeater's output. I would guess that channel 1 is their primary channel, so going simplex on it would mean they were transmitting on the repeater's output freq (452.37500) and not the input (457.37500).
I've seen the input on radios as another channel. Years ago when I was on a rescue squad, we were stuck in a "hole" and were not able to hit the repeater to call EOC, but we were less then a mile from the EOC. I simply went simplex with EOC, bypassing the repeater and they were able to hear us perfectly. The PD in the same city had channel 1 for the primary channel for the repeater, channel 2 for the secondary channel for the repeater, channel 3 as channel 1's simplex and channel 4 and channel 2's simplex.