What they were looking for is the Real-time face detector implemented directly in the C code which is available only for the commercial version of the library (https://pixlab.io/downloads).

This may be an unreasonable risk-reward tradeoff. On the upside, you saved some money. On the downside, you risked (a) an international incident, (b) being cut off from future updates and (c) bringing unnecessary attention to your surveillance project. Much better tradecraft to try buying cleanly, thereby incentivizing everyone on both sides to co-operate, while keeping the shady tactics as a back-up plan.

But, if you're a nation state, I'm sure just throwing money at the open market will work too. I'm sure that for every company that refuse defence contracts, there are a number that will hapilly build a pink fluffy-looking drone with built in facial recognition, 250 grams of explosives and a proximity fuse. Or, just be willing to sell surveillance tech to authorative governments.