ACA had impacts on employer plans as well. It is not crazy to suggest that the excessive rise in health care costs across the board is due to the ACA in large part, even if your plan is employer sponsored.
It's not a completely ridiculous theory, but it's pretty crazy. The data is clear that premiums are being driven by cost increases across the board. Moreover, employer plans are in completely different risk pools than individual plans. The only place they meet is in the insurer's balance sheet - they charge enough on all plans to cover their payouts plus the (regulated) profit margin.
You can argue that cost increases are due to all of those previously uninsured sick people who are now insured and costing the rest of us money, but that's both wrong (costs have been going up faster than inflation for decades), and a pretty awful worldview.
The GP comment is just another example of how there's a ton of uninformed anger on this issue. People are spitting mad because they're realizing that health care is becoming really expensive, and they think the ACA is to blame because they heard about the ACA last. The amount of actual understanding approaches zero, because few people pay for their own healthcare in the USA.
I kind of want the GOP to just burn everything down and expose everyone to the full pain of this absurd system (in true, "free market" fashion). We'll have a political revolution overnight.