While there is not evidence of "everyone" purchasing bunkers in Europe, there is a significant increase in bunkers (according to the first source, there was a 3000% increase in interest of purchasing), which could be what was being described as a "boom" in what was once a small market. If there is truly no evidence of a "bunker boom", It could be insightful to add to the fact check evidence suggesting otherwise, such as stats from other sources, especially if you believe these sources are biased/misleading.