Another NGO that is critical of Israel, HaMoked, keeps track of the number of security prisoners in Israel by month. (B'Tselem used to but says that they can no longer get the information under Israel's Freedom of Information Act. It is unclear how HaMoked does.)
The first thing you notice is that the number of prisoners has stayed roughly the same between April and today.
The second thing is that the number of security prisoners actually decreased during the time period in question, between April and June, indicating that however many people Israel arrested were not placed in prison (unless Israel released a similar number of prisoners, which seems highly unlikely.)
