That makes no sense at all. Venus orbits closer to the Sun than Earth does. This means when looking at Venus we are always looking towards the Sun. For this reason Venus is very visible during sunrise or sunset (depending on the position of Venus), so the Sun is behind the horizon whilst Venus isn't. As soon as the Sun gets above the horizon it becomes much harder to see Venus, because the Sun is much brighter in the sky and Venus is near it.
When Venus is far away from the Sun, as we see it in our sky, it's also a very pronounced crescent, so they wouldn't mistake it for a balloon.
This sounds like a story someone made up somewhere, but has now been repeated so many times it's hard to tell if it's real or not.
In 1960 the US DEW Line mistakenly thought the Soviet Union had launched a nuclear strike when it detected the moon rising. Luckily cooler heads prevailed when the radar operators quickly realized both the reported launch locations and target locations were crescent shapes and moving east to west as the moon rose.
This is the kind of thing I think of when I hear the UFO people imply that information from pilots must be accurate, because they're experts. Fuck no. Experts make mistakes all the time. Sometimes things just get confusing and you make mistakes.
Some time after that incident a known Japanese spy walked right by a military checkpoint by simply goatse.
("Is that the Japanese spy we are looking for?" - "Don't be silly, that is clearly Uranus, if we make another mistake like that we will never hear the end it it.")