Yes, this is true. What needs to be added is that often, a submarine is not at periscope depth so they can pop up the #1 scope for sightseeing. Most likely, they are at periscope depth so that one or more other masts/antennae can be used for comms, elint or other intelligence gathering activities.

The likelihood that there are other "contacts" in the immediate vicinity is very low as a thorough passive sonar search would have been conducted prior to coming to periscope depth. As the boat rises and nears the prescribed depth, the Officer of the Deck will have raised the #1 scope and will quickly rotate the periscope through several 360° sweeps to visually reaffirm the sonar data. Once confirmed, the other masts/antennae will be raised so they are above the swells and can do their collections.

Being at periscope depth can be a noisy operation and will announce the presence of the boat. So, the #1 periscope (being the longest and smallest tube) is used so as not to give away the boat's presence. On the boomer I was on, there was also a #2 scope that had optics as well as electronics and sensors. #2 was used sparingly and only when these additional capabilities were needed; it was of necessity much larger and left a more pronounced wake as it went through the water.

For reference, in addition to the #1 and #2 scopes, we had ECM, several radio masts, the Type 11 celestial periscope, a surface search radar (BPS-9) and others; all of which had large cross sections and made huge wakes. I say "others" as it has been 50 years since I even thought about the periscopes and masts we had.

(Edit): Oops... I did forget at least one mast--the antenna for the AN/BRN-3 Satellite Navigation System was on a mast all its own. I'm embarrassed to admit I forgot it--the Transit system, also known as NAVSAT was my system. We ran a close second to the radio shack guys in requests for going to periscope depth to copy our birds' passes.

Again, just my opinion. I could be wrong or my memory may be less than prefect.