Not necessarily. The resolution of each grid cell changes with the zoom level, you can see the resolution in the legend of each apparent fishing effort layer (for example in the screenshot, 120 km2 is the approximate grid cell area at equator). Each grid cell adds fishing effort for the area of the cell, so to make sure to know if the fishing activity was inside or outside EEZ limits, you should analyze each vessel track for more detail.
To analyze the vessel track in more detail, click on the grid cell and then click on the vessel to add the track to the map. You can hover your mouse over the timebar to see vessel movements over time. You can also see fishing, port, loitering and encounter events along the track for more information.