When the dog marks the spot where the boar is after working around the area, he does not really expect him to prepare the latter.
The majority of game tends to choose to flee from hunting dogs, but it is not uncommon for wild boars to make the opposite choice and rush straight towards the dog(s).
This reaction is very dangerous for dogs if the boar in front is particularly well armed, but fortunately this is not always the case. Dogs, whether equipped with a protective vest or not, are often agile enough to dodge the assaults of suids, as is the case in this video.
This dog will certainly get away with a good fright because, seeing his assured and confident position, he probably did not expect the boar to come straight at him.