The simple answer is No, it is not Kufr
Hiding the sin
Exposing the sin makes it worse, because it consists of two sins, the initial sin in addition to exposing it,
Abu Hurairah (May Allah be pleased with him) reported:
Messenger of Allah (ﷺ) said, "Every one of my followers will be
forgiven except those who expose (openly) their wrongdoings. An
example of this is that of a man who commits a sin at night which
Allah has covered for him, and in the morning, he would say (to
people): "I committed such and such sin last night,' while Allah had
kept it a secret. During the night Allah has covered it up but in the
morning he tears up the cover provided by Allah Himself."
[Al-Bukhari and Muslim].
Thus the sinner who did his sins as a result of conquering self or the whispers of the devil or the predominance of fancy, and he try to hide his sin out of shame and shyness of Allah and people, is no doubt better than who expose them..
Not Ashamed of Allah
Saying that it’s important to know that not exposing the sins does not contradict with the other hadith which discusses a different case
The case of those who are not ashamed of Allah and do not avoid his sacred limits (Maharemoh), but watching the people and take into account the human beings, those who are when they are among people they show their good side, and once become away of people's observation they violate Allah's commands.
narrated Thawban that the Prophet (ﷺ) said:
“I certainly know people of my nation who will come on the Day of
Resurrection with good deeds like the mountains of Tihamah, but Allah
will make them like scattered dust.” Thawban said: “O Messenger of
Allah, describe them to us and tell us more, so that we will not
become of them unknowingly.” He said: “They are your brothers and from
your race, worshipping at night as you do, but they will be people
who, when they are alone, transgress the sacred limits of Allah.”