My opinion he is clueless. Tips curl up from light stress and potassium deficiency which leads to lights stress also underwatering. Leaves will droop and be swollen from over watering, you will get deficiency not tip burn from over watering. And yours kinda looking a bit papery and dry
Coco in small pots sgould be done without perlite but bigger pots benefit for the extra drainage and aeration (needed no beneficial yes). Sounds like he is a soil or peat grower. The benefit to cocos growth rates are its ability to hold and exchange o2 with a low saturation zone and higher area of o2 rich media
Ask him this next time... why do plants have issues when overwatered... its not the water that roots have an issue with... think about it. How do plants grow with roots fully submerged in hydro? It's because over watering is not to much water its lack of oxygen... ppl just call it over watering but that's the cause not the reason.
He so must not understand that pot size and shape play a role.
Be happy to have him make an account and discus openly with him if he likes.
Again it sounds like a soil grower giving advice on coco. While in the early stages of growth some dry back won't hurt letting coco dry is a no no... now I can say you probably won't see an issue... until there is one. Which is usually a couple weeks into flower and it fucks you grow to hell. Just a warning while some hydro store guys are pretty good. Most are label readers and salesmen repeating what they hear from randoms in the store. Not all but most. Generally the owners have a better idea but even then sometimes not.