Opportunity cost means exactly what he thinks it means. The idea is that it might look cheaper to develop technology in-house, but if it takes longer to build than buy, the company is losing out on sales during the time it's building. It also could be losing out on early-mover advantages. Those reductions in revenue are called the opportunity cost (because the size of the opportunity is smaller).

Factoring in the opportunity cost may make buying a more attractive option. Keeping opportunity cost in mind can help the seller get a much better price than they would if they just considered the acquirer's cost to duplicate heir technology.