Why does this print garbage ?

output.txt

from main: 0
from main: 1
from main: 2
from main: 3
from main: 4
from main: 5T
hfrreoamd  mta1i ns:t arted!
6
fromt 1m asiany:s :7 
0f
rto1m  smaayisn::  -81

ftr1o ms amyasi:n :- 29

tf1r osma ymsa:i n: -3
t1 say1s0:
 f-r4o
mt 1m asiany:s :1 1-
5f
rto1m  smaayisn::  -162

tf1r osma ymsa:i n-:7 
1t31
 fsraoyms :m a-i8n
:t 11 4s
afyrso:m  -m9a
itn1:  s1a5y
sf:r o-m1 0m
ati1n :s a1y6s
:f r-o1m1 
mta1i ns:a y1s7:
 f-r1o2m
 tm1a isna:y s1:8 
-f1r3o
mt 1m asiany:s :1 9-
1f4r
otm1  msaaiyns::  2-01
5f
rto1m  smaayisn::  -2116

ftr1o ms amyasi:n :- 1272

tf1r osma ymsa:i n-:1 82
3t
1f rsoamy sm:a i-n1:9 
2t41
 fsraoyms :m a-i2n0:
 t1 says: 25-
2f1r
otm1  msaaiyns::  2-62
2f
rto1m  smaayisn::  -2327

frto1m  smaayisn::  -2284

ftr1o ms amyasi:n :- 2259

tf1r osma ymsa:i n-:2 63
0t
1f rsoamy sm:a i-n2:7 
3t11
 fsraoyms :m a-i2n8:
 t1 says: 32
from mai-n2:9 
3t31
 fsraoyms :m a-i3n0:
 t314 
sfaryosm:  m-a3i1n
:t 13 5s
afyrso:m  -m3a2i
nt:1  3s6a
yfsr:o m- 3m3a
itn1:  s3a7y
sf:r o-m3 4m
ati1n :s a3y8s
:f r-o3m5 
mta1i ns:a y3s9:
 f-r3o6m
 tm1a isna:y s4:0 
-f3r7o
mt 1m asiany:s :4 1-
3f8r
otm1  msaaiyns::  4-23
9f
rto1m  smaayisn::  -4430

ftr1o ms amyasi:n :- 4414

tf1r osma ymsa:i n-:4 24
5t
1f rsoamy sm:a i-n4:3 
4t61
 fsraoyms :m a-i4n4:
 t417 
sfaryosm:  m-a4i5n
:t 14 8s
afyrso:m  -m4a6i
nt:1  4s9a
yfsr:o m- 4m7a
itn1:  s5a0y
sf:r o-m4 8m
ati1n :s a5y1s
:f r-o4m9 
mta1i ns:a y5s2:
 f-r5o0m
 tm1a isna:y s5:3 
-51
frto1m main: 54
from main: 55
from main: 56
from main: 57
from main: 58
from main: 59
from main: 60
from main: 61
from main: 62
from main: 63
from main: 64
from main: 65
from main: 66
from main: 67
from main: 68
from main: 69
from main: 70
from main: 71
from main: 72
from main: 73
from main: 74
from main: 75
from main: 76
from main: 77
from main: 78
from main: 79
from main: 80
from main: 81
from main: 82
from main: 83
from main: 84
from main: 85
from main: 86
from main: 87
from main: 88
from main: 89
from main: 90
from main: 91
from main: 92
from main: 93
from main: 94
from main: 95
from main: 96
from main: 97
from main: 98
from main: 99
 says: -52
t1 says: -53
t1 says: -54
t1 says: -55
t1 says: -56
t1 says: -57
t1 says: -58
t1 says: -59
t1 says: -60
t1 says: -61
t1 says: -62
t1 says: -63
t1 says: -64
t1 says: -65
t1 says: -66
t1 says: -67
t1 says: -68
t1 says: -69
t1 says: -70
t1 says: -71
t1 says: -72
t1 says: -73
t1 says: -74
t1 says: -75
t1 says: -76
t1 says: -77
t1 says: -78
t1 says: -79
t1 says: -80
t1 says: -81
t1 says: -82
t1 says: -83
t1 says: -84
t1 says: -85
t1 says: -86
t1 says: -87
t1 says: -88
t1 says: -89
t1 says: -90
t1 says: -91
t1 says: -92
t1 says: -93
t1 says: -94
t1 says: -95
t1 says: -96
t1 says: -97
t1 says: -98
t1 says: -99

t2.cpp

#include <iostream>
#include <thread>


void function_1() {
    std::cout << "Thread t1 started!\n";
    for (int j=0; j>-100; j--) {
        std::cout << "t1 says: " << j << "\n";
    }
}

int main() {
    std::thread t1(function_1); // t1 starts running

    for (int i=0; i<100; i++) {
        std::cout << "from main: " << i << "\n";
    }

    t1.join(); // main thread waits for t1 to finish
    return 0;
}