The book of Acts is a historical description of the formation of the church (called out assembly (ἐκκλησία)), who were mostly Gentiles, but were also Jews who were convicted and believed, like those in the day of Pentecost. The book of Acts describes how the church demonstrated their coping with the persecution and perseverance in the newly found faith.
The words in English "to all" are actually one in the Greek (πᾶσιν), which is the dative masculine plural, which technically means that it was given to all men. Contextually, there is no indication that anyone referred to in the paragraph was an unbeliever, but rather believers who were in the close fellowship described in verse 46.
- Side note:
While Christians ought to bless those outside of the church, we are called to do so especially unto those of the faith (Galatians 6:10).
In those days, the church was being established and therefore, the practice would have been for those who were added unto the church by the Lord. Contextually, it will be describing how the 3000 souls were added and how they (v.42)"continued steadfastly in the apostles’ doctrine and fellowship, and in breaking of bread, and in prayers. (V.43) And fear came upon every soul: and many wonders and signs were done by the apostles."
So, since there is no further mention of how that act would have affected the unbelievers who received anything from these believers, we can safely conclude that the comments are to describe the methodology the church members used to deal with the needs of that time; and therefore believers are those who received/shared goods among themselves, as any of the believers representing their families had need.